This application is based on Patent Application No. 2000-72401 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a focus detecting device.
2. Description of the Related Art
In conventional single-lens reflex cameras, an area on the photographic screen for accomplishing the autofocus (AF) operation (hereinafter referred to as the xe2x80x9cauto focus areaxe2x80x9d) is disposed vertically or horizontally relative to the rectangular shaped photographic screen, but in recent years an oblique AF area disposition has come to be necessary for wide range and the like.
When the AF area is oblique, however, focus detection accuracy is decreased compared to the vertical/horizontal dispositions.
That is, when luminous flux passes through a main mirror disposed at an inclination relative to the optical axis, the luminous flux is refracted within the main mirror, such that the image forming position is shifted and aberration is generated. Conventionally, optical elements are positioned behind the main mirror without regard for this aberration.
The arrangement of the focus detection area at an inclination refers the case wherein a direction connecting two photoreceptor sensors is neither parallel nor perpendicular relative to a plane including the normal line of the main mirror and the optical axis.
In general, such optical elements disposed behind the main mirror include a sub-mirror for refracting the optical path, aperture mask for capturing only the luminous flux of the AF area, separator lens for forming an image with the luminous flux of the AF area, and photoreceptor sensor (e.g., a charge-coupled device (CCD) sensor) for receiving the luminous flux forming an image on the AF area.
The present inventors ascertained that decreased focus detection accuracy is caused by the increased influence of aberration particularly when the AF area is disposed at an inclination.
Accordingly, the technical object of the present invention of eliminating these problems is attained by providing a focus detecting device which does not decrease focus detection accuracy even when the AF area is disposed at an inclination.
The technical objects of the present invention are attained by the focus detecting device of the present invention comprising, in a focus detecting device for detecting the focus of a taking lens using the luminous flux of a focus detection area disposed at an inclination relative to the photographic field,
a first optical element for transmitting luminous flux transmitted through a taking lens and disposed at an inclination relative to the optical axis behind the taking lens; and
a second optical element arranged at a position for correcting aberration generated by luminous flux transmitted through the first optical element and disposed behind the first optical element.
The present invention arranges the second optical element so as to correct aberration of luminous flux generated by the first optical element. In this way aberration influence is nil or slight, and the focus detection accuracy is not decreased even when the AF area is disposed at an inclination.
The technical objects of the present invention are attained by another focus detecting device of the present invention comprising, in a focus detecting device for detecting the focus of a taking lens using the luminous flux of a focus detection area disposed at an inclination relative to the photographic field,
a first optical element for transmitting luminous flux transmitted through a taking lens and disposed at an inclination relative to the optical axis behind the taking lens; and
a second optical element disposed at an inclination relative to the optical axis and disposed behind the first optical element
wherein the second optical element is provided with a first surface through which enters the luminous flux transmitted through the first optical element, and a second surface for reflecting the luminous flux transmitted through the first surface.
The technical objects of the present invention are attained by another focus detecting device of the present invention comprising, in a focus detecting device for detecting the focus of a taking lens using the luminous flux of a focus detection area disposed at an inclination relative to the photographic field,
a first optical element for transmitting luminous flux transmitted through a taking lens and disposed at an inclination relative to the optical axis behind the taking lens; and
a second optical element for transmitting light transmitted through the first optical element and disposed at an inclination in the opposite direction of the first optical element.